Radioactive Decay. Lab Report 5
2
Joseph Berg Luwa Matthews Sunday, May 16, 2010 Investigating the Radioactive Decay of Cobalt Abstract: The purpose of this lab was to determine the decay constant and half-life of Cobalt and how its decay rate varies with angle and distance. Cobalt coins of different ages were placed in front of a Geiger counter and the decay rates were measured at different angles and distances from the Geiger counter. Using different methods of data analysis, the half-life of the Cobalt sample was found to be 5.2 years and 4.88 years, with respective decay constants of 0.133 Hz and 0.1419 Hz. The rate of decay was found not to be proportional to 1 r 2 . Also, the decay rate varies with angle. Experimental Procedure: This experiment was carried out with four Co coins of different ages ranging from a few months to twenty years. Initially, the zero point decay rates of each of the coins were measured multiple times for 10 seconds each. Assuming that all four coins had the same starting rate, the decay rate measured was plotted against the relative age of each coin. The decay rate of the youngest coin was taken as the initial rate. See figure 1. The decay constant was found to be 0.133 Hz, with a half-life of 5.2 years. Another method of data analysis involved taking pairs of coins and determining the decay constant for each using equation 1. −ln ( R old R new ) ∆t (1)
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Transcript of Radioactive Decay. Lab Report 5
Joseph Berg
Luwa Matthews
Sunday, May 16, 2010
Investigating the Radioactive Decay of Cobalt
Abstract:
The purpose of this lab was to determine the decay constant and half-life of Cobalt and how its decay rate varies with angle and distance. Cobalt coins of different ages were placed in front of a Geiger counter and the decay rates were measured at different angles and distances from the Geiger counter. Using different methods of data analysis, the half-life of the Cobalt sample was found to be 5.2 years and 4.88 years, with respective decay constants of 0.133 Hz and 0.1419 Hz. The rate of decay was found
not to be proportional to 1
r2. Also, the decay rate varies with angle.
Experimental Procedure:
This experiment was carried out with four Co coins of different ages ranging from a few months to twenty years. Initially, the zero point decay rates of each of the coins were measured multiple times for 10 seconds each. Assuming that all four coins had the same starting rate, the decay rate measured was plotted against the relative age of each coin. The decay rate of the youngest coin was taken as the initial rate. See figure 1. The decay constant was found to be 0.133 Hz, with a half-life of 5.2 years.
Another method of data analysis involved taking pairs of coins and determining the decay constant for each using equation 1.
−ln( RoldRnew )
∆ t
(1)
where R refers to the zero point decay rates of the coins and ∆ t is the difference in their ages.
The average decay rate was found to be 0.1419 Hz and the half-life was 4.88 years.
The decay rate was found to vary with angle. See figure 3.
The decay rate was found to vary with distance, but not by 1
r2, which tended to fall off too
quickly. This can be attributed to the decay rate varying with angle. See figure 2, which has an exponential decay curve fitted to it.
Conclusion:
Using various methods, the he half-life of the Cobalt sample was found to be 5.2 years, 5.23 years, and 4.58 years.
The corresponding decay constants were found to be 0.133 Hz and 0.1419 Hz.
The decay rate of the cobalt sample was found not to be proportional to 1
r2.
